This invention relates to a hydraulic pressure control device for a vehicle, particularly one including an electronic control device to compute optimum braking conditions based on information from various sensors to make possible various controls such as applying brakes even while the driver is not operating brakes, generating braking force larger than the amount the driver is operating to produce, or lowering the braking force even though the driver has no intension of relaxing the brakes, with a simple structure. This invention also relates to a vehicle brake system using it.
A so-called brake-by-wire type vehicle brake system has been developed in which in order to electrically control braking forces applied to the vehicle, the amount of braking applied by the driver and the hydraulic pressure generated by the brake operation are converted to electric signals and the hydraulic pressure generated in the power line (that is, pressure source including a power-driven pump) is adjusted to a value corresponding to the electric signals and supplied to the wheel brakes.
Also, in a general one of brake systems of this kind, if a solenoid valve in the passage connecting the power line with the wheel brakes should not open due to failure of electric line, even if pressure is accumulated in the power line, it becomes impossible to effectively use it for braking. Thus, the present inventors have developed a brake system as shown in FIG. 10.
In the device of FIG. 10, a proportional pressure control valve 60 is provided in a passage 49 extending from a pressure source 50 provided with pumps 46 driven by a motor 45, a pressure accumulator 47 and a hydraulic pressure sensor 48 to the wheel brakes 38 (added symbols specify the respective wheels, namely FR shows front right wheel; FL, front left wheel; RR, rear right; and RL, rear left). When the brake pedal 31 is depressed, a passage 34 extending from a master cylinder 32 to the wheel brakes 38 is shut off with a solenoid valve 35, the amount of applying the brake pedal 31 and the hydraulic pressure generated in the master cylinder 32 are detected by a stroke sensor 44 and a hydraulic pressure sensor 39, respectively, and converted to electric signals in an electronic control device 40, and a current corresponding to the electric signals is supplied to the proportional pressure control valve 60 to adjust the hydraulic pressure for the wheel brakes 38 to a value corresponding to the brake operating amount with the proportional pressure control valve 60.
In the proportional pressure control valve 60, as shown in FIG. 11, a spool valve 62 is inserted in a housing 61 having an input port 61a, output port 61b and discharge port 61c. The spool valve 62 is driven by a magnetic force generated by activating a coil 66a of a solenoid 66 to selectively connect the output port 61b to the input port 61a or the discharge port 61c and adjust the degrees of opening of passages formed between a shoulder portion on the outer periphery of the spool valve 62 and edge portions of the respective ports. The spool valve 62 has opposed pressure-bearing surfaces having a difference in area which is equal to the sectional area of a pin 65 inserted into a pin hole 64. Thus, assuming that the hydraulic pressure P introduced through the input port 61a is P, the force of a return spring 63 is F, the current supplied to the coil 66a is I, and the sectional area of the pin 65 is S, the thrust force acting against the spool valve 62 balances at the position where the following formula is met:
Pxc2x7S+F=aI2 (a is a constant) 
and the spool valve 62 stops at this position.
Replacing the above formula,
P=(axc2x7I2xe2x88x92F)/S 
In this formula, a and S are constants. If the spring constant is ignored, F can also be regarded as a constant. Thus, the hydraulic pressure P is proportional to the square of the current I and depends on the amount of applying the brake pedal 31.
In the system of FIG. 10, if the electromagnetic force is not produced in the proportional pressure control valve 60 due to failure of the electric line, a solenoid valve 43 in a passage 42 opens, so that the hydraulic pressure generated in the master cylinder 32 acts on the proportional pressure control valve 60. By the hydraulic pressure, an auxiliary piston 67 in FIG. 11 is pushed and the movement of the auxiliary piston 67 is transmitted to the spool valve 62 to adjust the position of the spool valve. Thus, the hydraulic pressure in the pressure source 50 is adjusted by the proportional pressure control valve 60, supplied to boost pistons 36 of FIG. 10, and the hydraulic pressure generated by the boost pistons 36 is supplied to the wheel brakes 38. Thus, even if the proportional pressure control valve 60 cannot be driven with a magnetic force, it is possible to apply the brakes by effectively using the hydraulic pressure in the pressure source 50.
Among brake systems developed by the present inventors, there is one in which during failure of the electric line or if the amount of applying the brake pedal exceeds a predetermined amount, the proportional pressure control valve (spool valve) is driven by the brake pedal force.
JP patent publication 2000-326839 also discloses a system in which during failure of the electric line, the spool valve is driven by the brake pedal force.
The brake system of FIG. 10, which was developed by the present inventors, needs a master cylinder and a plurality of solenoid valves. It also needs a stroke simulator 52 of FIG. 10 for taking in brake fluid fed from the master cylinder while the system is operating normally, and a solenoid valve 51 that closes the inlet side passage of the simulator during failure of the electric line. This incurs complicatedness of the structure and cost increase.
With the earlier developed system in which the spool of the proportional pressure control valve can be moved by the brake pedal in an emergency, since the spool is driven by the brake pedal only in an emergency in which the spool cannot be driven with an electromagnetic force or if the amount of applying the brake pedal exceeds a predetermined amount, electronic control is indispensable during normal braking. For one in which the spool is driven by the brake pedal in an emergency, a clutch for separating the spool valve from the brake pedal in a normal state is needed. On the other hand, one in which the spool is driven by the brake pedal after the amount of applying the brake pedal has exceeded a predetermined amount has a problem that responsiveness lowers in an emergency.
The system disclosed in JP publication 2000-326839 is also provided with a mechanism for preventing the movement of the brake pedal from being transmitted to the spool valve in a normal state. This complicates the structure. Also, with this system, since a hydraulic pressure generating device for adjusting pressure is provided independently of the brake pedal and the brake pedal force is transmitted to a lever in the hydraulic pressure generating device through a wire, the layout of the instruments is also complicated.
Thus, in view of reliability and cost, it is required to reduce elements that can cause a failure and cost increase and to improve responsiveness not only in a normal state but in an emergency.
On the other hand, if one tries to perform various kinds of controls, it is necessary that both control based on the intension of the driver and control by judgment of the electronic control device, separate from the intension of the driver, can be performed.
An object of this invention is to answer these requirements with a system that employs a proportional pressure control valve and is simple in structure.
According to this invention, there is provided a hydraulic pressure control device for a vehicle comprising a housing formed with an input port, an output port and a discharge port, a proportional pressure control valve having a spool valve and a return spring for biasing the spool valve, the spool valve being adapted to bring the output port into communication with the discharge port and shut off the input port while not in operation, a solenoid for generating a spool-driving force corresponding to a current supplied thereto, and a spring through which the brake pedal is coupled to the spool valve of the proportional pressure control valve, the spool valve being moved to a balance point where the spool-driving force produced by the solenoid, a thrust force produced when the spool valve bears introduced hydraulic pressures on its opposed pressure-bearing surfaces having a difference in area, and the force of the return spring, balance with an external force applied opposite thereto, to change over the connection between the output port and the discharge port and adjust the degree of opening of a passage therebetween and change over the connection between the input port and the output port and adjust the degree of opening of a passage therebetween, whereby both non-electrical pressure adjustment by the operation of the brake pedal and electrical pressure adjustment by the solenoid can be done.
For such a device, the following arrangements 1)-4) are conceivable.
1) The solenoid is a pressure-increasing solenoid and the driving force produced by the solenoid is applied to the spool valve in the same direction as the spool-push-in force by the brake pedal.
2) The solenoid is a pressure-reducing solenoid and the driving force produced by the solenoid is applied to the spool valve in the opposite direction to the spool-push-in force by the brake pedal.
3) The proportional pressure control valve is adapted to have its output characteristics offset by a predetermined amount in a direction opposite to the force produced by the driving force of the solenoid.
4) Both of a pressure-increasing solenoid and a pressure-reducing solenoid are provided, and the spool push-in force by the brake pedal and the driving force produced by the pressure-increasing solenoid are applied in the same direction, and the driving force generated by the pressure-reducing solenoid is applied in the opposite direction to the spool push-in force by the brake pedal.
5) A permanent magnet is provided which applies a magnetic force to one of the end faces of the spool valve, and by reversing the direction of current supplied to the solenoid, forces attracting and repelling relative to the permanent magnet are produced in the spool valve.
There is also provided a vehicle brake system comprising a reservoir for storing brake fluid, a pressure source for storing brake fluid supplied from the reservoir with its pressure increased, wheel brakes, the hydraulic pressure control device as described above with the input port communicating with the pressure source, the output port with the wheel brakes, and the discharge port with the reservoir, and an electronic control device for computing optimum braking conditions based on information from various sensors and controlling the solenoid of the hydraulic pressure control device based on the results of computation.
Because the hydraulic pressure control device of this invention can perform, not only in an emergency but in a normal state, non-electrical pressure adjustment in which no electromagnetic force is used by transmitting the brake pedal force to the spool valve, it is possible to perform control based on the will of the driver without electronic control.
Also, since it needs no clutch for separating the spool valve from the brake pedal or no means for stopping the transmission of force in a normal state, it is possible to simplify the structure and reduce the cost. Also, since the proportional pressure control valve is integrated with the brake pedal, it is possible to simplify the piping and reduce the installation space.
Further, since the brake pedal force is applied to the spool valve from the beginning of operation, there will be no delay in response even during failure of the electric line.
With the device having a pressure-increasing solenoid, it is possible not only to generate braking force corresponding to the amount of braking, but to generate more braking force than that obtained by depressing the brake pedal and to perform automatic braking.
With the device having a pressure-decreasing solenoid, it is possible to reduce the braking force while the brake pedal is being depressed and to perform regenerative blending brake control in which in response to regenerative braking carried out in an electric vehicle, the hydraulic braking force is weakened to increase the regenerative efficiency.
If both a pressure-increasing solenoid and a pressure-reducing solenoid are provided, it is possible to cope with all of the above-described control requirements. The device in which a permanent magnet is added to the device having only one of the two solenoids has similar functions to the device having both the pressure-increasing solenoid and pressure-reducing solenoid.
With the device having output characteristics offset relative to the driving force by the solenoid, by balancing the offsetting force with the force of the solenoid to make the offsetting force apparently zero and adjusting the force of the solenoid, it is possible to perform substantially pressure-reducing control with a pressure-increasing solenoid or perform substantially pressure-increasing control with a pressure-reducing solenoid. Namely, the device having a single solenoid can have similar functions to the device having both a pressure-increasing solenoid and a pressure-reducing solenoid.
Also, since the vehicle brake system of this invention can perform adjustment of the wheel brake pressure based on the command from an electronic control device only with a single hydraulic pressure control device, it is simple, inexpensive, fewer in failure factors, and good in responsiveness in an emergency. Various kinds of controls are also possible.